This invention relates to the pruning of cordon-trained grapevines and more particularly to a method and apparatus whereby such grapevines can be pruned mechanically.
A high percentage of grapevines throughout California and in some other parts of the world are trained to what is called a "bi-lateral cordon trellising system". This is a system where each vine along a row thereof is trained vertically up a stake, is then formed into a "Y", and each branch of the "Y" is trained along a horizontal trellis wire extending along the row. As the permanent branches, or cordon, matures, they form two long permanent arms of the vine in line with and along the trellis wire and at approximately equal distances from the ground throughout their length. Protruding from the bi-lateral cordon along its lengths are permanent spurs which are formed as the vine grows each year. These spurs of annual growth are cut back at pruning time to a particular length which is determined by the number of buds desired per spur. During the next growing season, the growth of the vine comes from each of these buds. At pruning time the following year, the growth from each bud is cut back again to result in a given number of buds per spur. As the vines grows and is pruned from year to year, these spurs become branches which progress further and further from the trellis wire or from the cordon attached thereon.
It has long been recognized that the vines should be pruned each year so that a controlled growth results in the next growing season to provide a desired balance between the amount of foliage growth and the amount of fruit grown on the vine. If the pruning leaves too many buds on the vine spurs, there will be an excessive number of bunches of grapes formed and the vine will put a relatively great amount of its energy into producing the fruit crop and a relatively small amount of its energy will be put into producing the vine growth and foliage. Since each leaf of the foliage is a nutrient factory supplying energy from the sun to the plant, too little foliage will result in the vine having insufficient energy to produce the excessive fruit crop. As a consequence the crop will have a low sugar content and poor quality.
On the other hand, if too few buds are left, too great an amount of energy of the plant will go into producing foliage. The fruit crop will have high sugar content and high quality but the crop amount will be small.
As is apparent, the conditions which is desired is one in which the foliage and crop growth is balanced to provide a maximum harvest of high quality grapes. The proper balance has always been controlled by pruning the spurs to leave a proper number of buds, the number of buds varying somewhat in accordance with the particular variety of grapes being grown.
The authoritative educators within the wine industry and the commercial viticulturalists have long contended that having a specific number of buds per spur throughout the length of the cordon is essential for quality, crop quantity and foliage balance. The practice then has been to prune the vines to leave a predetermined number of spurs per cordon and a predetermined number of buds per spur. Because of the way a vine grows in nature, the spurs have a relatively random growth pattern and there are different, and random, distances between adjacent buds on the spurs. As a consequence, pruning of the spurs to have an equal number of buds on each spur will result in spurs to considerably different lengths. The traditional pruning method, therefore, can only be accomplished by hand with the buds on each spur being counted so that the spur will be pruned to the desired length. As is apparent, traditional pruning is tedious and time consuming.